In some way's it's a sequel to Ace Combats 5 and 04. It features some of the main nation's featured in the previous games, as well as Stonehenge from Ace Combat 04. Realistically we'll have to wait until the release to see just how sequel like that makes the game. But like what Oran said, no Ace Combat game is really a direct sequel to another one.
The only two Ace Combat games that are directly connected are Ace Combat 5 and Ace Combat Zero.
All other Ace Combat games pretty much feature individual, disconnected stories. There are lots of references in Ace Combat 7 to some of the older games, especially Ace Combat 04, 5, and AHL/3D (on the 3DS), but it's not a direct sequel of any one particular game.